We propose to investigate the roles and synergistic actions of retinoic acid and cyclic-AMP in the maturation of human myeloid leukemia cells. Activation of cAMP-dependent protein kinases and alteration in their subcellular localization and level is the likely mechanism by which retinoids and cAMP induce granulocytic differentiation of human myeloid cell lines and fresh explants of some human myeloid leukemias. We will determine the subcellular localization to Type I and Type II cAMP-dependent protein kinase using photoaffinity labeling and gel electrophoresis. Protein phosphorylation patterns in isolated nuclei will be determined and correlated with granulocytic maturation and expression of specific genes (myc, n-ras, lysozyme, HLA-B). The long term objective of this proposal is to begin to understand the biochemical events underlying myeloid differentiation. During the first portion of this project, core courses will be taken in the Duke University Program in Cell and Molecular Biology. The major scientific disciplines involves in this study are Hematology, Oncology, Cell Biology, and Biochemistry. In vitro maturation of promyelocytic leukemia cells serves as a model for bone marrow differentiation. Studies such as this may define the molecular defects leading to cessation of myeloid differentiation and hence leukemia. The proposal is health-related because it explores a pathway of differentiation which is blocked in leukemia. Agents active as inducers of cell differentiation are now finding clinical application in the experimental treatment of leukemia and other malignancies.